This project aims to characterize the receptors and signal transduction mechanisms of angiotensin II (AII) in adrenal glomerulosa and other AII target cells. We recently cloned a calcium-mobilizing AII receptor (AT1b) from the adrenal gland and are currently analyzing the structural factors involved in ligand binding, G-protein coupling, and receptor internalization. To facilitate such studies, the cDNA encoding a calcium-mobilizing amphibian AII receptor that does not recognize non- peptide antagonists of mammalian AII receptors was cloned from the Xenopus laevis myocardium. Knowledge of the structure of this unique AII receptor, which has about 60% amino acid similarity with the mammalian AT1 receptors, will be utilized in studies on mutant forms of the two receptors to identify the residues and sequences that are involved in the ligand binding domains of the receptor. In glomerulosa cells, AII was found to act through AT1 receptors to induce the expression of several early growth response genes, including c-fos, c-jun, JunB, and Krox 24, acting through elevation of cytoplasmic calcium and activation of protein kinase C. The signaling requirements of the secretory and "nuclear" responses of glomerulosa cells differed in that the latter did not require the presence of extracellular Ca2+ and were fully induced by only a brief exposure to the hormone. These findings, and studies on mitogenesis in stably transfected adrenal Y1 cells expressing AT1a and AT1b receptor subtypes, are identifying the signaling mechanisms by which AII controls the secretory and growth responses of adrenal glomerulosa cells.